Lesson 09: Managing Users and Privileges in MySQL

Notes/errata/updates for Chapter 9:
See the official book errata at http://tahaghoghi.com/LearningMySQL/errata.php – Chapter 9 includes pages 297 – 350.

In the fourth paragraph of this chapter, starting with “Most applications don’t need superuser privileges for day-to-day activities” they give you some reasons why you want to create users without the SUPER privilege. There are better reasons than the book gives, which are at the MySQL Manual page for the SUPER privilege.

In the section “Creating and Using New Users” (p. 300) they say “There’s no limit on password length, but we recommend using eight or fewer characters because this avoids problems with system libraries on some platforms.” You should ignore this, this book was written in 2006 and modern system libraries can handle more than 8 characters in a password. Also ignore it when they say the same thing in the section “Understanding and Changing Passwords” (p. 324).

In the section “Creating a New Remote User” at the very end (p. 214), it talks about using % as a host wildcard character. I want to point out that if there are no ACL’s set for a given host, MySQL will reject ALL connections from that host – even “telnet host 3306” will fail. So if you avoid using %, you are slightly more secure.

In the “Anonymous Users” section (p. 315), one fact that is not mentioned is that for all users, including the anonymous user, any database named “test” or that starts with “test_” can be accessed and manipulated. So an anonymous user can create tables in the “test” database (or even “test_application”) and fill it full of data, causing a denial of service when the disk eventually fills up. This fact is mentioned later in the chapter in the “Default User Configuration” section under “Linux and Mac OS X”, but it should be known earlier.

The “mysqlaccess” utility described in the section of that name (p. 320) is usually not used. These days, folks prefer the pt-show-grants tool. Here is a blog post with some examples of pt-show-grants.

In the section on “Removing Users” (p. 324), it says that if all the privileges are revoked, and a user only has GRANT USAGE, “This means the user can still connect, but has no privileges when she does.” This is untrue, as mentioned before, everyone can access and manipulate databases starting with “test”.

The section “Managing Privileges with SQL” is deprecated (p. 339-346, up to and including “Activating Privileges”). It used to be, back when this was written, that few people used the GRANT statements and more people directly manipulated the tables. These days, it’s the other way around, and due to problems like SQL injection, there are safeguards in place – for example, if you change the host of a user with an ALTER TABLE on the mysql.user table, the user will have all privileges dropped. Just about the only thing direct querying is used for, is to find who has the Super_priv variable set to ‘Y’ in the user table.

Supplemental material: I have a video presentation on security which includes ACLs and there are accompanying PDF slides.

Topics covered:
Creating and dropping local and remote users
Different MySQL privileges
SUPER privilege
GRANT and REVOKE syntax
Hosts and wildcards
Anonymous and default users
Checking privileges
Password management
Basic user security
Resource limit controls

Reference/Quick Links for MySQL Marinate

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